The present invention relates to a method in a compact press section of a paper machine which includes a compact press roll combination, the rolls of which form at least two press nips with each other through which a paper web runs, by which method the fabrics in the press section and/or the press rolls of the compact press roll combination can be easily replaced. The method is applied in a frame construction for the press section which includes, in the direction of the run of the paper web, a front frame situated before the roll combination and a rear frame situated after the roll combination.
The invention also relates to a frame construction in a compact paper machine press section suitable for use in the practice of the method. The frame construction is for press section which includes a compact press roll combination whose press rolls form at least two and preferably three or more press nips with each other, the paper web running between the press nips, preferably as a closed draw.
In the frame construction of conventional compact press sections of paper machines, such as in the Sym-Press paper machine press section available from Valmet Oy of Finland, front and rear frames are provided before and after the compact press roll combination which are permanently connected to each other by horizontal beams located at both the operating and service sides of the paper machine. As used herein, "front frame" means the frame part that is situated before the compact press roll combination in the direction of web run through the press section and on which the upper press roll, conventionally a suction roll, of the first press nip is usually mounted. Correspondingly, "rear frame" means the frame part which is situated after the press roll combination.
Conventional frame constructions for compact paper machine press sections present difficulties in connection with the replacement of the press fabrics and press rolls. These problems have become more serious as the widths of the paper machines have increased since the press rolls are longer and heavier. Moreover, additional problems have been created by the increasing use of press fabrics formed of plastic materials. When formed of plastic, the press fabrics tend to be substantially rigid in the transverse direction which prevents the press fabrics from being compressed into a small volume, since this would cause the fabrics to become wrinkled and therefore not usable.
In an attempt to overcome the problems described above, Beloit Corporation of Beloit, Wis. has suggested a frame construction, designated as its "flip-top" construction, wherein either the top part of the front frame or the top part of the rear frame can be opened by rotating it about a pivot shaft whose axis is parallel to the transverse direction of the paper machine and which is situated above the press rolls. As a consequence of this construction, the two top parts of the frames cannot be opened at the same time.
In order to replace the pick-up fabric of a press section incorporating a "flip-top" frame construction, which fabric usually functions as the press fabric in the first and second press nips, the top part of the front frame is opened. During this procedure, however, the top part of the rear frame must be locked since the top part of the front frame, when opened, is supported on the top part of the rear frame. In a corresponding manner, the top part of the rear frame can be opened, such as in connection with the replacement of the press fabric in the third press nip, only when the top part of the front frame is closed and locked in position. The lower fabric of the first nip, which runs mainly in the basement space, is replaced by means of conventional arrangements.
The "flip-top" frame construction described above can be characterized as a type of "drawbridge" which is openable at an articulated joint which is situated in the middle of the drawbrige directly above the compact roll combination and wherein only one-half of the bridge can be opened at any one time.
The fact that the articulated joint of the "flip-top" frame construction is situated immediately above the compact press roll combination has been found to be a drawback in that this construction does not greatly facilitate the replacement of the press rolls. Rather, the press rolls must be replaced in the conventional manner by shifting them in their axial directions to the side of the paper machine. Such axial shifting requires that the grasping point at which the roll is supported on the hooks of a traverse crane must change from time to time. The press rolls must be shifted a distance equal to their entire length to the service side of the paper machine thereby requiring that the width of the aisle at the service side of the machine must be at least equal to the length of the rolls, e.g., about 8 to 10 meters. Absent this requirment, the aisle at the service side of the paper machine would not have to be so wide. It would be highly advantageous from the viewpoint of reducing the cost of construction of the paper machine hall to be able to reduce the width dimension of the aisle at the service side of the paper machine.
Another drawback of the "flip-top" frame construction described above is that when one of the top parts of the frame is opened, only a single felt can be replaced. If, after replacement of one felt, it is desired to replace another felt, it is necessary to close and lock the initially opened top frame part and then unlock and open the other top frame part. Consequently, the replacement of felts as well as press rolls in a press section provided in a frame construction of the type described above is a relatively lengthy procedure thereby increasing the downtime of the paper machine.
The downtime of the press section is also increased during replacement of felt and rolls due to the fact that the grasping point of the crane must be changed several times during the fabric or roll replacement operation.
Conventional methods used in the replacement of felts and rolls in press sections mounted in prior art frame constructions are difficult and slow for the additional reason that a sufficiently large open space has not been available for the replacement operations, particularly in the region above the rolls in the press section. It has therefore been necessary to perform the work in a very limited space thereby increasing both the time required to effect the roll and/or felt replacement as well as the hazards inherent in the operation.